Railway Vehicle Derailment Research Articles

Measures against Flange Climb Derailment of Railway Vehicles

Measures against Flange Climb Derailment of Railway Vehicles

Effect of curved track support failure on vehicle derailment

In order to investigate the effect of curved track support failure on railway vehicle derailment, a coupled vehicle–track dynamic model is put forward. In the model, the vehicle and the structure under rails are, respectively, modelled as a multi-body system, and the rail is modelled with a Timoshenko beam rested on the discrete sleepers. The lateral, vertical, and torsional deformations of the beam are taken into account. The model also considers the effect of the discrete support by sleepers on the coupling dynamics of the vehicle and track. The sleepers are assumed to move backward at a constant speed to simulate the vehicle running along the track at the same speed. In the calculation of the coupled vehicle and track dynamics, the normal forces of the wheels/rails are calculated using the Hertzian contact theory and their creep forces are determined with the nonlinear creep theory by Shen et al [Z.Y. Shen, J.K. Hedrick, and J.A. Elkins, A comparison of alternative creep-force models for rail vehicle dynamic analysis, Proceedings of the 8th IAVSD Symposium, Cambridge, MA, 1984, pp. 591–605]. The motion equations of the vehicle/track are solved by means of an explicit integration method. The failure of the components of the curved track is simulated by changing the track stiffness and damping along the track. The cases where zero to six supports of the curved rails fail are considered. The transient derailment coefficients are calculated. They are, respectively, the ratio of the wheel/rail lateral force to the vertical force and the wheel load reduction. The contact points of the wheels/rails are in detail analysed and used to evaluate the risk of the vehicle derailment. Also, the present work investigates the effect of friction coefficient, axle load and vehicle speed on the derailments under the condition of track failure. The numerical results obtained indicate that the failure of track supports has a great influence on the whole vehicle running safety.

Probabilistic Model for Predicting Rail Breaks and Controlling Risk of Derailment

A model is developed to analyze the risk of derailment of railway vehicles by using a probabilistic approach to model the development of rail defects leading to rail breaks and further to derailment. The risk of derailment is measured by the expected number of rail breaks multiplied by the severity of rail break. To evaluate the risk, four submodels are combined to predict the rate of occurrence of rail defects and breaks. These submodels include one to predict the expected number of weld defects, considering the effect of rail repair; a fatigue model of the rails; and a grinding model to take into account removal of defects through maintenance. The fourth submodel concerns the impact of inspections that are imperfect and of nonconstant frequency. The performance and application of the proposed combined model are illustrated by an example that shows the effectiveness of alternative measures in reducing the risk of derailment. It also shows that the proposed model can be used as a tool for quantitatively evaluating the risk of derailment and for decision making on control of the risk.

Effect of Disabled Fastening Systems and Ballast on Vehicle Derailment

The effect of disabled fastening systems and ballast on railway vehicle derailment is investigated by developing a nonsymmetrical coupled vehicle/track model. In the model a half passenger car is considered, and modeled with a multi-body system with 18 degrees of freedom, which runs on a tangent track at a constant speed. The tangent track is modeled as two elastic beams by discrete nonsymmetrical supporters modeling fastening systems, sleepers, and ballasts. The normal contact forces between wheels and rails are described by Hertzian elastic contact theory, and the tangential forces by the nonlinear creep theory of Shen et al. (Proceedings of the 8th IAVSD Symposium, Cambridge, MA, pp. 591–605). In the numerical analysis, the disabled rail fastening, rail pad, and ballast, on one and two sides of the track are, respectively, considered. Through a detailed analysis, derailment coefficients and the track state variations are obtained. The derailment coefficients are defined as the ratio of the lateral force to the vertical force of the wheel and rail (indicated by L∕V), duration of L∕V, and rate of the wheel load reduction (indicated by ΔV∕V), respectively. The variations of the contact points on the wheel treads, the track gauge, the track cross-level, and rail turnover angle are present in the paper. The numerical results obtained indicate that the failure of rail supports has a great influence on the vehicle running safety.

Comparison of Results of Calculations and Measurements of DYSAF-tests, a research project to investigate safety limits of Derailment at High Speeds

Test runs have been carried out in Velim, Czech Republic, to analyse derailment conditions at higher speeds up to 160 kph. In the research program ‘DYSAF’ a test running gear was developed which enabled to test derailment of a wheelset in guiding and unloaded conditions. With the aid of a lateral force actuator static and dynamic Y/Q derailment situations were measured for different velocities and angle of attack. In this paper a comparison of test and simulation results of the multi body program MEDYNA is presented.Identifying the parameters of nominal wheel loads of the test running gear and friction coefficients in tread and flange simulation results show a very good and promising agreement for the compared signals. Only higher frequency terms are lacking. To include them dynamic properties of track, hydraulic device and wheel roundness have to be improved.Derailment simulation with a MBS tool is a possibility to analyse derailment cases and to develop safety criteria against derailment of railway vehicles. Necessary is a wheel-rail element, which can describe multi non-elliptic contact patches in tread and flange, which can describe creepages in curved contact patches and which uses an extended creep force theory for non-elliptic contact patches. The wheel-rail element of ArgeCare is such an element.

Safety Criteria for Evaluation of Railway Vehicle Derailment.

Criteria for evaluating safety of railway vehicles concerning derailment are reviewed. In the case of quasi-static wheel climb derailment, the safety criteria in current use are available. Recently oscillatory wheel load fluctuations of considerable amplitude have been observed on Shinkansen vehicles running at high speeds, but there were no established evaluation methods for the dynamic derailment under such a specific condition. Based on a study on these dynamic phenomena through computer simulation, we propose to use the time duration of Y/Q in order to assess the safety against derailment. Moreover, the necessity to control the right to left static wheel load unbalance ratio and its limit value on assembling bogies are suggested in this paper with field data obtained from turnout running tests.